Method for producing a non-woven fabric

ABSTRACT

A non-woven continuous fabric comprises a plurality of discrete, laterally extending ribbon elements which are connected with continuous, longitudinally extending elements to form a netting which may be united with one or more layers of a continuous sheet plastics material orientated in the longitudinal direction of the fabric while at least the ribbon elements of the netting are also longitudinally orientated, i.e., in the lateral direction of the fabric. The fabric has been subjected to a needle punching operation causing the orientated materials thereof to fibrillate. A fiber fleece may be incorporated in the fabric. A method of producing the fabric comprises winding a continuous, longitudinally orientated ribbon of plastics material helically upon a plurality of thread- or ribbon-shaped secondary elements to form a netting which may be laid together with one or more sheets of longitudinally orientated plastics material to form a web assembly which subsequently is subjected to a needle punching operation. An apparatus for making the fabric comprises means for jointly feeding a netting and at least one sheet in superposed relationship and a needle punching device operating on the assembly of the netting and the sheet or sheets.

United States Patent 1191 Lerche-Svendsen 1 1 Jan. 36, 1973 [75] Inventor: Flemming Lerche-Svendsen, 2920 Charlottenlund, Denmark [73] Assignee: Aktieselskabet Denmark 221 Filed: March 17, 1971 21 Appl.No.: 125,043

Fibertex, Aalborg,

[30] Foreign Application Priority Data March 20, 1970 Denmark ..l442/70 [56] References Cited UNITED STATES PATENTS 3,428,506 2/l969 Johnstone ..l6l/l54 X 3,6l6,l68 l0/l97l Johnstone ..I6l/l54 Primary Examiner-William A. Powell Attorney-Sughrue, Rothwell, Mion, Zinn & Macpeak [57] ABSTRACT A non-woven continuous fabric comprises a plurality of discrete, laterally extending ribbon elements which are connected with continuous, longitudinally extending elements to form a netting which may be united with one or more layers of a continuous sheet plastics material orientated in the longitudinal direction of the fabric while at least the ribbon elements of the netting are also longitudinally orientated, i.e., in the lateral direction of the fabric. The fabric has been subjected to a needle punching operation causing the orientated materials thereof to fibrillate. A fiber fleece may be incorporated in the fabric. A method of producing the fabric comprises winding a continuous, longitudinally orientated ribbon of plastics material helically upon a plurality of threador ribbon-shaped secondary elements to form a netting which may be laid together with one or more sheets of longitudinally orientated plastics material to form a web assembly which subsequently is subjected to a needle punching operation. An apparatus for making the fabric comprises means for jointly feeding a netting and at least one sheet in superposed relationship and a needle punching device operating on the assembly of the netting and the sheet or sheets.

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20a 20b 37b 37a 9 METHOD FOR PRODUCING A NON-WOVEN FABRIC BACKGROUND OF THE INVENTION This invention relates to a non-woven, web or ribhon-shaped fabric comprising two or more superposed layers of fibrillatable plastic sheet or film, especially but not exclusively polypropylene sheet, which layers have received a monoaxial or substantially monoaxial orientation in directions which are different in the different layers. After superposition of the layers, their materials have been caused to fibrillate by a needlepunching operation.

In British Pat. specification No. 1,176,662, it is described how a fabric of this type can be manufactured in a relatively simple manner by directly piercing the superposed sheets with needles. The fabric may be used as a floor or wall covering, or it may be employed as a backing layer in carpets or other pile fabrics in which pile yarns are tufted to the backing layer. While it is easy to produce a molecular orientation in the longitudinal direction of the plastic sheets to be incorporated into the fabric, since this may be obtained simply by stretching the sheet which is extruded as a continuous web, it is considerably more difficult to achieve an orientation at an angle to the longitudinal direction, particularly in the transverse direction. It is, for example, known to extrude the sheet in the form of a hose which is subsequently stretched in its longitudinal direction and slit or cut open along a helical line. The method is complicated and consequently the starting materials of the above-mentioned non-woven fabric and, hence, the finished fabric, become relatively expensive, in particular if the desired width of the fabric is large so that it is necessary to provide correspondingly large webs or sheets, the orientation of which differs from the longitudinal direction thereof.

SUMMARY OF THE INVENTION According to the present invention there is provided a nonwoven fabric comprising a continuous webshaped assembly of at least two superposed layers each of which comprises a fibrillatable and at least substantially monoaxially orientated plastics material, said layers having different directions of orientation, and the layers of said assembly having been subjected to fibrillation by means of a needle punching treatment of the assembly, wherein at least one of said superposed layers comprises a plurality of ribbon-shaped primary elements having a direction of orientation at least substantially perpendicular to the longitudinal direction of said assembly and joined together with secondary filamentary elements extending at least substantially in the longitudinal direction of said assembly so that said primary and secondary elements form a continuous netting structure.

By employing a netting structure as referred to, it becomes possible, in a very simple manner to introduce in the fabric'a layer of a plastics sheet material which is orientated perpendicularly to the longitudinal or advancing direction of the fabric, since said layer is incorporated as elements of a netting which can be produced continuously at a high speed and, consequently, at a low price.

The other sheet or sheets of the fabric may, due to said orientation of the netting elements, be orientated only in their longitudinally direction. Consequently all layers or components of the composite fabric may be produced by very simple methods, and it is possible to obtain an angle of between the directions of orientation which, in turn, results in a homogeneous distribution of the directions of the fibers in the finished fabric and uniform strength and elongation properties lengthwise and crosswise of the fabric. At the same time, the netting structure constitutes a convenient means for temporarily connecting the elements stretched or orientated transversely of the finished fabric before these elements are permanently joined together with the longitudinal sheet layer or layers. It will be understood in this connection that when reference is made to a netting structure, this term also embraces a structure in which, at least the ribbons extending in the lateral or transverse direction of the finished fabric are completely contiguous or only slightly spaced from each other, so that due to their joining with the longitudinally extending netting elements, they constitute a substantially continuous sheet extending across the entire width of the fabric.

It is expedient to make the primary and secondary netting elements from the same material and with substantially identical crimping characteristic since this contributes to increase the desired homogeneity of the finished fabric.

The invention also relates to a method of producing a non-woven fabric, which method comprises providing at least one continuous layer of a longitudinally orientated plastics sheet material and a continuous netting structure comprising discrete primary ribbon-shaped netting elements extending in the transverse direction of said netting structure and orientated in said direction, and continuous secondary netting elements extending longitudinally of said netting structure, jointly advancing said layer and netting structure in the common longitudinal direction and laying them together to form a web assembly, and piercing said web assembly by means of punching needles so as to cause at least the sheet material and the primary ribbon elements of the netting structure to fibrillate.

The secondary netting elements may be produced by slitting a continuously advancing web or sheet into narrow ribbons, thus simplifying the manufacturing process in that it is then possible to place the starting material for these elements in one or a few rolls at the side of the netting producing machine, which rolls require less space than the big bobbin frames that would be necessary if the elements were formed as threads and unreeled from individual thread bobbins.

A plurality of webs may be arranged in at least two layers with the individual webs of one, layer laterally overlapping the webs of another layer, and when such layers are laid together with the netting, a fabric of large width and very uniform thickness may be produced.

Before a subsequent to superposing the sheet layer or layers and the netting to be incorporated into the fabric, a thin fiber fleece may be incorporated into the fabric, which fleece is pinned or punched together with the other elements of the fabric. Such a fiber fleece may be utilized not only for producing a desired surface of the finished fabric, but also for establishing the desired joining together of the longitudinal and transverse layers of material, first by the needle-punching operation and subsequently in a more permanent way in response to a stabilizing treatment in a heated calender or in a heating furnace or oven. After the needle-punching, the fleece serves to bond the fibers formed by fibrillation, in that the fleece fibers, due to the action of the needles, are caused to interlock with and around each other and to become entangled with the short lengths of fiber or fibrils projecting from the sheet material. Consequently it is not necessary to effect any substantial tearing of the sheet fibers by means of the punching needles which would reduce the strength of the fabric.

The fiber fleece may be fed in the same direction of advance as the sheet layer or layers and the netting, whereby local variations in the thickness of the fleece in the finished fabric are avoided, which could arise by cross-laying the fleece transversely across the web assembly.

It is preferred that the needle-punching be carried out with less than appr. 425 punches per square inch. A significant disintegration or breakdown of the monoaxially orientated molecular structure of the sheet layers and a weakening resulting therefrom of the strength and dimensional stability of the fabric is hereby avoided.

The invention also provides an apparatus for producing a continuous non-woven fabric which apparatus comprises a plurality of supplies including at least one continuous sheet of at least substantially monoaxially orientated plastics material and a continuous netting having discrete primary ribbon-shaped netting elements extending transversely of the netting and being orientated in that direction, and continuous secondary netting elements intersecting and joined to said primary netting elements, means for continuously and jointly feeding said sheet and said netting in their common longitudinal direction and in superposed relationship, means for connecting together said sheet and said netting to form a continuous web assembly, and a needle punching device having a plurality of punching needles and means for reciprocating said needles through said web assembly transversely to the surfaces thereof.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows an elevation of a machine for producing nettings which forms part of an apparatus embodying the present invention,

FIG. 2 shows the machine seen in the direction of arrow II in FIG. 1 with certain details omitted for the sake of clarity,

FIG. 3 shows a section through two layers of sheet material which are joined together with netting produced in the machine shown in FIGS. 1 and 2,

FIG. 4 shows a section corresponding to FIG. 3 with a different mutual placing of the webs of the two layers,

FIG. 5 shows an elevation of the apparatus without the machine shown in FIGS. 1 and 2,

FIG. 6 shows a modified apparatus corresponding to FIG. 5, in which the needle-punching machine has been left out, and

FIG. 7 is a view seen in the direction of arrow VII in FIG. 5 and showing the individual layers of the web assembly being advanced towards the needle-punching machine prior to entering the said machine.

It is pointed out that the figures of the drawings are rather schematical and only illustrate such details of the invention which are believed to be necessary for the understanding thereof, while elements that are conventional and well-known in the art, have been omitted or only indicated very diagrammatically.

DETAILED DESCRIPTION FIGS. 1 and 2 illustrate a machine which is employed in the production of a netting of intersecting plastics ribbons or threads and which, in broad outlines, is constructed in conformity with that shown in US. Pat. No. 3,384,521. The machine has a frame 1 with a vertical stand 2 which, by means of members not shown in detail, e.g., radial arms, carries a circular cylindrical support 3 for the netting formed. Support 3 may be made in the form of a sheet ring and of heating-conducting material which has heating elements (not shown) on the inside. Below support 3, a guide ring 4 which may be cooled is secured to stand or stands 2. One or more guide means 5 are situated below the guide ring and, during the downward travel of the netting, the guide means gradually transform its cross section from circular into oblong until the netting is slit or cut open at the bottom of the machine by means of two knives 6 so that two flat netting structures are formed which, via guide rolls 7 supported in frame 1, are wound each on a separate take-up roll 8.

A frame 9 is mounted at the side of the machine, and one or more rolls 10 of a monoaxially stretched plastics sheet, e.g., polypropylene, are rotatably supported in frame 9. From each roll 10, a sheet 11 is unwound past a cutting device 12 having a plurality of relatively closely-spaced knives 13 which cut up the sheet into a large number of narrow ribbons 14. As described in US. Pat. No. 3,384,521, the ribbons are then conducted into the netting-producing machine via guide rolls 15 in frame 1 and up across the topmost edge of support 3, which may be provided with slots or other guides determining the mutual location of the ribbons in the netting which is formed by wrapping transverse ribbons around ribbons 14, as described in the said patent specification.

For laying or depositing the transverse ribbons, the machine has a vertical, centrally located shaft 16 which is caused to rotate by means of a motor (not shown) in frame 1. From bobbins 17 supported on bobbin holders 18 in a bobbin frame 19 mounted at the side of the machine, two ribbons 20a and 20b are unreeled. The ribbons consist of monoaxially stretched plastic material and, as shown, the top ribbon 20a is led directly to the topmost end of shaft 16 and from there to a rotating thread guide 21 mounted on an arm 22 secured to shaft 16. The bottom ribbon 20b is led into frame 1 at the bottom thereof and vertical upwards through the hollow shaft 16, from the topmost end ofwhich it is led out to another thread guide 21 which also rotates together with shaft 16.

When shaft 16 rotates with thread guides 21, while, at the same time the longitudinal ribbons are continuously advanced by the pull from the driving mechanism (not shown) of take-up rolls 8 as described in US Pat. No. 3,384,521, a netting comprising ribbons 14 and 20 which are joined at their points of intersection, is formed on support 3. The joining may be effected by means of an adhesive which, with the aid of means (not shown), is applied to ribbons 14 and/or and is activated by heating support 3. The joining may also be effected solely by heating the thermoplastic starting materials.

The part of the apparatus shown in FIG. 5 comprises three roller frames 24 mounted behind one another at the supply end of a belt conveyor 25. As shown in FIG. 5, one of the frames 24, for instance the one located farthest away from the conveyor, may accommodate a roll 8 of the netting 23 produced in the machine described above. Each of the other two frames accommodates one or more rolls 26 of monoaxially orientated plastics sheet, e.g., polypropylene sheet. All the sheets and the netting are pulled forwardly from the rotatably supported rolls and across guide rollers 27 associated with frames 24 and conveyor 25, for example, by means of one or more driven feed rollers 28 associated with conveyor and engaging the upper face of the web assembly formed by said sheets and netting on the conveyor.

At the discharge end of the conveyor, a needlepunching machine 29 known per se is mounted. The machine is only indicated quite diagrammatically as having a frame 30 and a needle unit 31 comprising a holder reciprocating in a vertical direction and a great number of needles 32 secured to the underside of the holder. The vertical movement of the needle unit is schematically indicated in FIG. 5 by way of a crank mechanism 33.

Between the supply end of conveyor 25 and needlepunching machine 29, there may, as shown in FIG. 5, be mounted a conveyor 34 for supplying a thin fiber fleece 39. The conveyor 34 may be adapted to receive the fiber fleece direct from a carding machine (not shown) and to transport it downwardly towards the superposed layers of sheet material and netting. When the lower or discharge end of conveyor 34 reciprocates transversely of conveyor 25, the fiber fleece is deposited continuously. on top'of the web assembly advancing towards and through the needle-punching machine, the needles of which thus penetrate both the fleece and the subjacent layer.

By the action of the needles 32 on the sheets and netting, these materials are split due to the preceding orientation stretching so that the materials fibrillate, whereby the finished fabric acquires the nature of a fabric made of fibers. Behind the needle-punching machine, the individual layers of the fabric may be permanently fixed to each other and stabilized by being passed through a heating calender or heating furnace. However, it is also possible, particularly when the above-mentioned fiber fleece is not deposited on the web assembly, to join the sheets and netting together prior to the needle-punching, for instance, by means of heated pressure rollers associated with conveyor 25 or by other suitable means.

FIGS. 3 and 4 show two different configurations of the two layers of plastics sheet that are unreeled or unwound from rolls 26. In FIG. 3, the webs 35 and 36 of the two layers are slightly displaced sideway or staggered in relation to each other, while the webs of each individual layer may be quite closely contiguous to each other. By joining the layers and the subsequent fibrillation, a fabric is thus formed which, except for two narrow edge zones, has a constant thickness and correspondingly an even distribution of the fibers formed by the needle-punching. In the configuration shown in FIG. 4, the said thinner edge zones have been avoided in that the staggering corresponds to half a web width. While the topmost layer thus consists of three equally wide webs 37a, the bottommost layer consists of two wide webs 37b and two edge webs 38 only half as wide.

Since the needle-punching of the superposed layers of material is primarily intended to produce the fibrillation of the stretched plastics materials, but only to a minor extent to cause the layers to stick together, it may be expedient to employ needles 32 having blunt ends, contrary to the normal needles used, e.g., in the production of needle felt, which are provided with projecting barbs. The needles 32 may be of polygonal, especially square or triangular cross section having concave sides forming longitudinal recesses. In the iongitudinal edges between the recesses there may be provided small incisions or steps acting as minute barbs which promote the entangling or matting of the fleece fibers with the fibers formed from the sheets without tearing or breaking the latter fibers to any substantial extent. Such needles are known and consequently it is deemed unnecessary to show them in detail.

FIG. 6 shows a modification of the apparatus illustrated in FIG. 5, in which a fiber fleece of melt-extruded fibers by way of preference of low denier, e.g., approximately 2-4, and possessing a strong tendency to crimping (high crimp), is produced in a known machine having a discharge conveyor 41 for the fleece, for example, the DOA machine well known to people skilled in the art, which is manufactured by Messrs. Spezialmaschinen Dr. 0. Angleitner, Linz-Wels, Austria, and which is able to supply a continuous fleece in a width of 5 meters or more. The machine, generally designated by 42, is mounted with its discharge conveyor 41 located above three frames 43 corresponding tofrarnes 24 in FIG. 5, so that the fleece is deposited or laidontop of a web assembly comprising three webs each advanced from its frame on a conveyor 44 which corresponds to conveyor 25 in FIG. 5 and which, in a similar manner, feeds the fleece and the webs forward to a needle-punching machine (not shown) and further on to a winding unit (not shown) for collecting the finished fabric.

As indicated in FIG. 6, the rolls supported in the three frames 43 may comprise two webs 45 and 46 each of which may extend continuously across the entire width of the fabric or consist of several juxtaposed sheets, cf. FIGS. 3-4, as well as a netting 23 which in the finished fabric is located between the sheets or webs 45 and 46. It will be understood that the netting as shown in FIG. 5 might form the outer layer of the finished fabric and that there may be more or fewer than two sheets or webs shown.

FIG. 7 shows, in a plan view, a section of the web assembly consisting of sheets, netting and fiber fleece as shown in FIG. 5, and the individual layers of the assembly have been successively cut away, so that all layers are seen from above. The fiber fleece 39 lies topmost and is indicated by a plurality of randomly dis tributed and strongly crimped fibers. Below this lie two continuous layers of sheets comprising sheets 37a and 37b, corresponding to those shown in FIG. 4, and the netting 23 with the transverse primary ribbons 20a and 20b and the longitudinal, secondary ribbons l4 lies bottommost. Even if the ribbons in FIG. 7 are shown spaced slightly apart, they may alternatively lie quite close to each other, particularly the primary ribbons 20a and 20b. The width of the individual ribbons may be of the order of magnitude of 1 cm. The superjacent sheets 37a and 37b will normally be considerably wider than shown in FIG. 7 which, however, is intended to illustrate clearly the lateral staggering of the individual sheets also shown in FIG. 4, rather than the relative dimensions of the elements of the fabric.

In FIG. 1 the bobbins 17 with the transverse or primary ribbons 20a and 20b are stationary, which has the advantage that the netting can be produced in a continuous operation since a fresh bobbin may be placed on the bobbin holder and the trailing end of the ribbon on one bobbin may be fixed to the leading end of the ribbon on the fresh bobbin during the unreeling of the first mentioned bobbin. However, when using conventional stationary bobbins, a twisting of the ribbons occurs when they are laid upon the longitudinal ribbons 14 and if such a twisting cannot be tolerated in the finished fabric it is advisable to employ special bobbins in which the ribbons have been wound or laid with a twist opposite to the twist occuring during the unwinding and with the same frequency or rate of twist. Alternatively the bobbins 17 may be driven in timed relationship with the rotary guides 21 and in that case it is necessary to stop operation each time the bobbins are empty.

It has been mentioned above that the longitudinal or secondary ribbons 14 of the netting are also made from orientated plastics. However, this is not mandatory since the primary function of these netting elements is to keep together the transverse ribbons of orientated plastics material until these latter can be joined together with the orientated sheets which extend longitudinally of the finished fabric. In principle, the longitudinal netting elements may be of any suitable kind and they may consist of threads instead of, as shown, ribbons, since with continuous sheets incorporated in the fabric they are not of primary importance to the strength and stability of the fabric. Other modifications are also possible within the scope of the invention. It would thus be possible to omit the sheet or sheets which, according to FIG. or 6, are combined with the netting and fiber fleece in which case the finished fabric would consist solely of a netting in which the longitudinal and transverse ribbons should then lie closely together, and of a fiber fleece covering the netting and joined together therewith. In such a case, it will be understood that both the longitudinal and the transverse ribbons ought to be produced of orientated sheet material. If the supply conveyor for the fiber fleece shown in FIG. 5 is mounted between two roller frames, the fleece would be located between two of the layers of material which are unwound form the rolls and subsequently joined together instead of, as shown, outermost in the finished fabric. The calendering operation of the needle-punched fabric as briefly referred to above can be carried out at a temperature below the melting point of the materials, e.g., at approximately 155 C. when using polypropylene as the principal constituent of the fabric and, in such a case, a pressure between the rollers in excess of lbs. per linear inch can be used, that is to say approximately 27 kp/cm. When the individual sheet layers of the fabric are produced from materials possessing the same crimping characteristic, as mentioned above, the heating during the calendering operation results in a uniform crimping in the longitudinal and transverse directions, whereas the fiber fleece (if present) may be crimped to a larger degree and thereby strengthen the inner cohesion of the fabric.

What is claimed is;

1. A method of producing a non-woven fabric, comprising providing at least one continuous layer of a longitudinal orientated plastics sheet material and a continuous netting structure comprising discrete primary ribbon-shaped netting elements extending in the transverse direction of said netting structure and orientated in said direction, and continuous secondary netting elements extending longitudinally of said netting structure, jointly advancing said layer and netting structure in the common longitudinal direction and laying them together to form a web assembly, and piercing said web assembly by means of punching needles so as to cause at least the sheet material and the primary ribbon elements of the netting structure to fibrillate.

2. A method as claimed in claim 1 comprising heating said sheet material and said netting to a softening temperature and joining them together in superposed relationship.

3. A method as claimed in claim 1, wherein an adhesive is applied between said sheet material and said netting to join them permanently together.

4. A method as claimed in claim 1, wherein said secondary netting elements are continuously advanced along a cylindrical supporting surface and said primary netting elements are helically wound in the form of a continuous ribbon around said secondary elements to form therewith a hose-like netting structure which is subsequently slit longitudinally and flattened.

5. A method as claimed in claim 4, wherein said secondary netting elements are made by longitudinally slitting a continuously advancing web of plastics material to form a plurality of narrow ribbons which are then led to said supporting surface.

6. A method as claimed in claim 1, in which at least two of said continuous layers are each composed of a plurality ofjuxtaposed webs located to that the webs of one layer laterally overlap webs of another layer.

7. A method as claimed in claim 1, in which a continuous thin fiber fleece is introduced into said web assembly prior to the needle punching operation and advanced together with said sheet layers and said netting structure so as to be subjected to said needle punching operation.

8. A method as claimed in claim 7, in which said fiber fleece comprises melt-extruded filamentary elements of low denier and high crimp.

9. A method as claimed in claim 7, in which said fiber fleece is supplied to said web assembly in the advancing direction thereof.

10. A method as claimed in claim 1, wherein the needle punching operation comprises not more than approximately 425 punches per square inch of the area of said web assembly.

* t I i 

1. A method of producing a non-woven fabric, comprising providing at least one continuous layer of a longitudinal orientated plastics sheet material and a continuous netting structure comprising discrete primary ribbon-shaped netting elements extending in the transverse direction of said netting structure and orientated in said direction, and continuous secondary netting elements extending longitudinally of said netting structure, jointly advancing said layer and netting structure in the common longitudinal direction and laying them together to form a web assembly, and piercing said web assembly by means of punching needles so as to cause at least the sheet material and the primary ribbon elements of the netting structure to fibrillate.
 1. A method of producing a non-woven fabric, comprising providing at least one continuous layer of a longitudinal orientated plastics sheet material and a continuous netting structure comprising discrete primary ribbon-shaped netting elements extending in the transverse direction of said netting structure and orientated in said direction, and continuous secondary netting elements extending longitudinally of said netting structure, jointly advancing said layer and netting structure in the common longitudinal direction and laying them together to form a web assembly, and piercing said web assembly by means of punching needles so as to cause at least the sheet material and the primary ribbon elements of the netting structure to fibrillate.
 2. A method as claimed in claim 1 comprising heating said sheet material and said netting to a softening temperature and joining them together in superposed relationship.
 3. A method as claimed in claim 1, wherein an adhesive is applied between said sheet material and said netting to join them permanently together.
 4. A method as claimed in claim 1, wherein said secondary netting elements are continuously advanced along a cylindrical supporting surface and said primary netting elements are helically wound in the form of a continuous ribbon around said secondary elements to form therewith a hose-like netting structure which is subsequently slit longitudinally and flattened.
 5. A method as claimed in claim 4, wherein said secondary netting elements are made by longitudinally slitting a continuously advancing web of plastics material to form a plurality of narrow ribbons which are then led to said supporting surface.
 6. A method as claimed in claim 1, in which at least two of said continuous layers are each composed of a plurality of juxtaposed webs located to that the webs of one layer laterally overlap webs of another layer.
 7. A method as claimed in claim 1, in which a continuous thin fiber fleece is introduced into said web assembly prior to the needle punching operation and advanced together with said sheeT layers and said netting structure so as to be subjected to said needle punching operation.
 8. A method as claimed in claim 7, in which said fiber fleece comprises melt-extruded filamentary elements of low denier and high crimp.
 9. A method as claimed in claim 7, in which said fiber fleece is supplied to said web assembly in the advancing direction thereof. 